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Nov. 15, 2011 -- Kids who spend hours a day playing video games may be hardwired to behave that way -- or their brains may have been altered as a result of all the gaming.

The answer is not yet clear, but when researchers compared the brains of 14-year-olds who played video games excessively to those who played less often, they found key differences in an area of the brain associated with reward and addiction.

The brain imaging study revealed that the structure and activity in the part of the brain associated with reward processing was bigger in frequent gamers.

Specifically, an area of the brain known as the ventral striatum -- considered key to motivation and reward -- had more gray matter in kids who played video games nine hours or more a week compared to those who spent less time gaming.

It was not clear if playing video games led to the increase or if kids with larger volumes of ventral striatum were more drawn to video games in the first place.

Researcher Simone Kuhn, PhD, of the University of Ghent in Belgium, says more research is needed to tease this out. But she says that it may be that people with larger ventral striatum volumes might derive more pleasure from playing video games.

Brain Scans for Video Game Players

The study included 154 German 14-year-olds who were asked about their video game habits. The teens underwent brain scans, and the researchers examined differences in their brains.

The study participants were considered frequent gamers if they reported playing more than nine hours a week or infrequent gamers if they spent less time playing video games.

The scans revealed that the frequent gamers had more gray matter volume in the part of the brain known for reward and addiction. And they also showed more evidence of brain activity in this region when they completed a gambling task designed to simulate winning a video game.

The findings suggest that people with more gray matter in this part of the brain might experience video gaming as more rewarding, Kuhn says.

The study is published online in Translational Psychiatry.

In an effort to determine if playing video games actually alters the brain, Kuhn and colleagues plan to study people who have not previously played them. The researchers plan to scan these people's brains before and several months after they are introduced to video gaming.

Video Games: Fun or Addictive?

Social psychologist Andrew Przybylski, PhD, who is a visiting fellow at the University of Essex in England, studies why people play video games.

Przybylski tells WebMD that the research as a whole does not suggest that video games are addictive the way cigarettes, alcohol, and drugs are.

He believes that for most people who enjoy them, video games are intensely pleasurable in the way that some people find golf and watching television on TV very pleasurable.

"I don't believe there is anything inherently addictive about video games any more than other things that people find fun," he says.